depends on the family.
if you do every ride, every show, every character meet up, check out the shops, eat, it would be more than a full day.
if you only want to do certain rides, of course it can be done on one day.
i always say there are more to the parks than just the rides.
if you go in the low season, the hours are shorter.
you couldn't do it all in one day if you took in everything in the park.
everyone tours parks differently.
for me, i can do AK in a half day.
others might say it takes them two full days to do that park.
what i find entertaining, others might not.